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tcp: count CLOSE-WAIT sockets for TCP_MIB_CURRESTAB

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According to RFC 1213, we should also take CLOSE-WAIT sockets into
consideration:

  "tcpCurrEstab OBJECT-TYPE
   ...
   The number of TCP connections for which the current state
   is either ESTABLISHED or CLOSE- WAIT."

After this, CurrEstab counter will display the total number of
ESTABLISHED and CLOSE-WAIT sockets.

The logic of counting
When we increment the counter?
a) if we change the state to ESTABLISHED.
b) if we change the state from SYN-RECEIVED to CLOSE-WAIT.

When we decrement the counter?
a) if the socket leaves ESTABLISHED and will never go into CLOSE-WAIT,
say, on the client side, changing from ESTABLISHED to FIN-WAIT-1.
b) if the socket leaves CLOSE-WAIT, say, on the server side, changing
from CLOSE-WAIT to LAST-ACK.

Please note: there are two chances that old state of socket can be changed
to CLOSE-WAIT in tcp_fin(). One is SYN-RECV, the other is ESTABLISHED.
So we have to take care of the former case.

Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Signed-off-by: Jason Xing <kernelxing@tencent.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jason Xing 2024-06-04 01:02:16 +08:00 committed by David S. Miller
parent 712115a24b
commit a46d0ea5c9
1 changed files with 5 additions and 1 deletions
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6
net/ipv4/tcp.c
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@ -2649,6 +2649,10 @@ void tcp_set_state(struct sock *sk, int state)
if (oldstate != TCP_ESTABLISHED)
TCP_INC_STATS(sock_net(sk), TCP_MIB_CURRESTAB);
break;
case TCP_CLOSE_WAIT:
if (oldstate == TCP_SYN_RECV)
TCP_INC_STATS(sock_net(sk), TCP_MIB_CURRESTAB);
break;
case TCP_CLOSE:
if (oldstate == TCP_CLOSE_WAIT || oldstate == TCP_ESTABLISHED)
@ -2660,7 +2664,7 @@ void tcp_set_state(struct sock *sk, int state)
inet_put_port(sk);
fallthrough;
default:
if (oldstate == TCP_ESTABLISHED)
if (oldstate == TCP_ESTABLISHED || oldstate == TCP_CLOSE_WAIT)
TCP_DEC_STATS(sock_net(sk), TCP_MIB_CURRESTAB);
}